Alrighty my Cosplay Prop buddies out there! I have a question for you!

now this is the first time I have EVER made a prop to this size.
And I have 0 knowledge on how to use power tools and such.
And now I am wondering.
How can I re enforce this bad boy?
it stands about 5 feet tall and is made out of Foam. The problem is that it wabbles and has no stability. I tried card bored for the center but it just made things worse.
Any ideas?

Ideally you would put wood in the center to grant additional stiffness, however if you have an aversion to tools you can coat the outside with fiberglass cloth/mat and resin. I did that for this foam prop and it was super solid. GL Happy cosplay!

You could try making an internal "skeleton" with a combination of cardboard and wire - a couple of coat hangers, twisted together to make a spiraling helix shape, will add a lot of internal strength. For even more internal strength, replace the cardboard with something sturdier like wood (as suggested above), MDF, or a plastic like Sintra.

An exoskeleton made out of something hard will also help. Fiberglass, Bondo, or good ol' paper mache.